Junction-type semiconductor device



J UNCTION-TYPE SEMICONDUCTOR DEVICE Hans Nagorsen, Berlin-Siemensstadt, Germany, assignor to Siemens-Schuckertwerke Aktiengesellschaft, Berlin- Siemensstadt and Erlangen, Germany, a corporation or Germany Application February 16, 1956, Serial No. 566,032 Claims priority, application Germany February 26, 1955 13 Claims. (Cl. 317-234 My invention relates to semiconductors of the junctionor area-type and, more particularly, to semiconductor devices of asymmetrical conductance such as rectifiers and transistors with a crystalline body of germanium, silicon or other semiconductor substance of similar character.

For such rectifiers and transistors, especially those of high operating efficiency, the required capability of carrying a large electric load per unit volume, makes it necessary to provide for best possible dissipation of the heat losses occurring in the device. This is so because the thermal load to which the crystalline semiconductor can be subjected is limited and,.if excessive, may result in permanent damage or temporary impairment of the semiconductor. It has, therefore, become known to pro vide for good heat transfer from the crystalline semiconductor-member proper directly to an adjacent body serving to conduct the heat away from the member.

It is an object of my invention to improve semiconductor devices of the above-mentioned type as to current-carrying capacity or loadability by improving the dissipation of heat from the semiconductor greatly beyond what has heretofore been attainable.

Another object of my invention is to minimize the manufacturing difficulties and mechanical sensitivity of such devices resulting from the fact that crystalline semiv conductor wafers or pellets of germanium, as used in such devices, are brittle and tend to crack or break under mechanical stress.

To achieve these objects, and in accordance with a featureof my invention, Idispose the crystalline semiconductor of the junction-type device between two good heat-conducting pressure bodies or clamping members of a holding device, and I provide between each electrode or electrode coating of the semiconductor and the adjacent face of the heat-conducting pressure body a coating of ductile conductive material, preferably ductile metal. The ductile coating is soldered, welded or otherwise fusion-joined with the pressure face of the body to form United States Patent part thereof and is in intimate face-to-face pressure engagement with the semiconductor electrode. The ductile coating is given such a minimum thickness that, when pressed against the electrode of the semiconductor, the

coating material enters into, and completely fills, the

usually irregular surface texture of the electrode' A material particularly suitable for the formation of such a coating on the face of the pressure body is indium (In), because indium is relatively soft and ductile when in normal condition. Consequently, with a sufiicient contact pressure between the pressure body and the electrode of the semiconductor member, a substantially perfect mutual adaptation is obtained between the two adjacent bodies. This is particularly the case if the electrode of the junction-type rectifier or transistor likewise consists of indium as is the case, for instance, with many junction-type rectifiers and transistors having a crystalline semiconductor member on thebasis of germanium 2 ,907,935 7 Patented Oct. 6, 1959 or semiconductor substance of similar character., I have found that under such conditions, the mutual good adaptation between the two indium bodies directly in contact with each other can readily be carried out to such a degree that practically a pressure fusion or welding of the two usually contacting surfaces will occur. In order to reliably secure this effect, it is necessary IQ give the coating of indium, fusion-joined with the pressure body for instance by a soldering process, a certain minimum thickness which has been found to be in the order of approximately 50.10- cm. With such a minimum thickness, sufficient material is available in the coating to penetrate into the irregular surface texture or pores of the electrode on the semiconductor member under the application of pressure between the coating and the electrode.

By virtue of the ductility and relative softness of indium, the provision of indium coatings according to the invention also improves the entire construction of a junction-type rectifier or transistor, particularly when the device is provided with a semiconductor on the basis of germanium which, as mentioned, is a rather brittle substance in the crystalline state. When the semiconductor member is put under pressure within the holding device, the mechanical stresses resulting from the mutual adaptation and compression of the inter-engaging surfaces, are taken up by the interior deformation of the two indium coatings. This prevents the transmission of direct mechanical stresses upon the wafer or pellet of germanium beyond the limit at which, due to brittleness of the crystal, mechanical damage may be caused to the crystal.

Aside from indium, other, similarly ductile metals may be used for the coatings on the pressure faces of the holding device. For instance, gold is similarly applicable.

According to general experience, the softness of metals increases with their degree of purity. Therefore, the metals to be used for the production of the pressure-face coatings according to the invention should be as pure as possible. I found that the degree of impurity in these metals should be smaller than 0.1% by weight, Le. a purity of more than 99.9% is required.

The above-mentioned and other objects, advantages and features of my invention will be apparent from the embodiment of a semiconductor device shown, partly in section, on the accompanying drawing.

In the illustrated device the rectifier or transistor member proper is denoted by 1. It consists of a crystalline semiconductor 1a in the shape of a circular wafer or pellet which is provided with two electrodes or electrode coatings 1b and 1c on opposite broad sides of the crystalline body.

When the semiconductor body 1a consists of germanium, the two electrodes 1b and 10 may consist of indium (In) and antimony (Sb) respectively. If the semiconductor 1a is made of silicon (Si), the electrode 1b may consist of aluminum (Al) and the electrode 1c of an alloy of gold (Au) and antimony (Sb). When the device consists of a transistor using germanium as the semiconductor material, then the two electrodes 1b and 10 may both consist of indium, and the base electrode, then located at 1d, may consist of an alloy of lead (Pb) and antimony (Sb).

The two electrodes 1b and 1c are in face-to-face contact with respective pressure bodies 2 and 3 of good heatconducting material such as copper, between which the semiconductor member 1 is clamped under pressure. The two pressure bodies 2 and 3 have their active pressure faces coated with respective layers 4 and 50f ductile metal, preferably indium or gold.

3 For convenience the above-mentioned examples of combinations of metals are tabulated below:

The two pressure bodies 2 and 3 are fastened by respective screw bolts 8 and 9 to angular supports 10 and 11 which in turn are fastened by means of screws 12, 13 to a base plate 14. Each pressure body 2, 3 is electrically insulated from the adjacent support 10 or 11 by an intermediate insulating layer 6 or 7 which is kept as thin as possible in order to provide for good heat transfer from pressure body to support. The screw bolts 8 and 9 are likewise insulated from the holders and may consist of insulating material. Also for promoting a good heat transfer, the pressure bodies 2 and 3 are shown to have conical or tapering shape, each having a relatively large surface adjacent to the support 10 or 11. The fastening screws 12 and 13 pass through elongated openings 15 in base plate 14 and can be displaced together with the respective supports 10, 11 for applying the desired clamping pressure to the semiconductor member 1 and securing the supports in the proper position.

Such a pressure device permits applying suflicient contact pressure between the semiconductor electrodes and the coatings 4, on the faces of the pressure bodies 2, 3 to secure a most intimate engagement between the mutually engaging faces and thus a good heat transfer between them. The structures 2, 3 or 10, 11 may be provided with cooling ribs or vanes in order to dissipate the heat, coming from the semiconductor member, to a surrounding cooling agent, for instance, the ambient air. The base plate 14 is provided with openings or bores to be traversed by fastening bolts 16, 17 with the aid of which the device can be mounted on the base or other structure 18 of an electrical apparatus or mounting frame.

It will be obvious to those skilled in the art, upon a study of this disclosure, that devices according to the invention can be modified in various ways as regards design and combination of materials, and may be given specific embodiments other than illustrated and described, without departing from the essence of my invention and within the scope of the claims annexed hereto.

I claim:

1. A junction-type semiconductor device, comprising a fiat crystalline body of semiconductor material selected from the group consisting of germanium and silicon, said semiconductor body having two electrode coatings on its respective broad sides, one of said coatings consisting of indium, a pressure device having two bodies of heat conducting metal in face-to-face relation to said respective electrode coatings, each of said bodies having a surface coating of ductile metal, one coating consisting of indium and being in contact with said indium electrode coating.

2. A junction-type semiconductor device of asymmetrical conductance, comprising a semiconductor crystal having two area electrodes on opposite sides of the crystal, a pressure device having two pressure bodies of heat conducting metal each having a face in pressure contact with one of said electrodes, and respective intermediate layers of ductile conductive substance fusion-joined with said bodies on said faces so as to form part of said bodies,

I at least one of said electrodes consisting of indium, and

one of said layers consisting of ductile metal in contact with said indium electrode, and support means for the bodies in heat conducting relation to the bodies, but elec-- trically insulated therefrom.

3. A junction-type semiconductor device of asymmetrical conductance, comprising a semiconductor crystal having two electrodes on opposite sides of the crystal,

4 a pressure device having two pressure bodies of heat conducting metal each having a face in pressure contact with one of said electrodes, and respective intermediate layers of ductile conductive substance fusion-joined with said bodies on said faces so as to form part of said bodies, at least one of said electrodes consisting of gold, and one of said layers consisting of ductile metal in contact with said gold electrode.

4 A junction-type semiconductor device of asym. metrical conductance, comprising a semiconductor plate comprising a crystal of a material of the group consisting of germanium and silicon having two area electrodes on opposite sides of the plate, a heat-dissipating device having two pressure bodies of heat conducting metal each having a face in wide area heat conducting relation to and in pressure-contact engagement with a respective one of the said electrodes of the semiconductor plate, each of said faces having a coating of ductile, heat conducting metal through which the pressure body is in intimate pressure engagement with the electrode of the semiconductor plate, and support means for the bodies in heat conducting relation to the bodies, but electrically insulated therefrom.

5. A junction-type semiconductor apparatus of asymmetrical conductance, comprising a semiconductor plate comprising a brittle single crystal having two electrodes on opposite sides of the plate, means for dissipating heat from and for supporting the plate comprising a device having two bodies of heat conducting metal each having a face in wide area heat conductive relation with respect to one of the said electrodes of the semiconductor plate, each of said faces having a coating of heat conducting, ductile, metallic material through which the respective body is in intimate engagement with the electrode of the semiconductor plate, said device further comprising two support elements mechanically connected to but electrically insulated from, and in heat conductive relation to, said bodies, and structural means for carrying the two support means a predetermined distance apart from each other.

6. A junction-type semiconductor apparatus of asymmetrical conductance, comprising a semiconductor plate comprising a crystal of the group consisting of germanium and silicon having two electrodes on opposite sides of the plate, means for dissipating heat from and for supporting the plate comprising a device having two bodies of heat conducting metal each having a face in wide area heat conductive relation with respect to one of the said electrodes of the semiconductor plate, each of said faces having a coating of heat conducting, ductile, metallic material through which the respective body is in intimate engagement with the electrode of the semiconductor plate, said device further comprising two support elements mechanically connected to but electrically insulated from, and in heat conductive relation to, said bodies, and structural means for carrying the two support means a predetermined distance apart from each other.

7. The semiconductor device defined in claim 6 in which the ductile metal is indium.

8. The semiconductor device defined in claim 6 in which the ductile metal is gold.

9. The semiconductor device defined in claim 4 in which the ductile metal on each of the said faces is fusion-joined therewith.

10. A junction-type semiconductor device of asymmetrical conductance, comprising a semiconductor crystal having two area electrodes on opposite sides of the crystal, a device having two massive blocks of heat conducting metal each having a face in wide area heat conducting relation to and in pressure contact with a respective one of said electrodes, each of said faces having a coating of indium.

11. A junction-type semiconductor device of asymmetrical conductance, comprising a semiconductor crystal having two area electrodes on opposite sides of the crystal, a device having two massive blocks of heat conducting metal each having a face in wide area heat conducting relation to and in pressure contact with a respective one of said electrodes, each of said faces having a coating of gold.

12. A junction-type semiconductor device of asymmetrical conductance, comprising a semiconductor crystal having two area electrodes on opposite sides of the crystal, a device having two massive blocks of heat conducting metal each having a face in wide area heat conducting relation to and in pressure contact with a respective one of said electrodes, each of said faces having a coating of indium, and support means for said blocks in heat conducting relation to the blocks, but electrically insulated therefrom.

13. A junction-type semiconductor device of asymmetrical conductance, comprising a semiconductor crystal having two area electrodes on opposite sides of the crystal,

a device having two massive blocks of heat conducting metal each having a face in wide area heat conducting relation to and in pressure contact with a respective one of said electrodes, each of said faces having a coating of gold, and support means for said blocks in heat conducting relation to the blocks, but electrically insulated therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 1,640,335 Grondahl Aug. 23, 1927 1,751,360 Ruben Mar. 18, 1930 1,809,925 Edwards June 16, 1931 1,894,821 Harty Jan. 17, 1933 2,380,880 Thompson, et a1 July 31, 1945 2,776,920 Dunlap Jan. 8, 1957 

1. A JUNCTION-TYPE SEMICONDUCTOR DEVICE, COMPRISING A FLAT CRYSTALLINE BODY A SEMICONDUCTOR MATERIAL SELECTED FROM THE GROUP CONSISTING OF GERMANIUM AND SILICON, SAID SEMICONDUCTOR BODY HAVIN TWO ELECTRODE COAGTING ON ITS RESPECTIVE BROAD SIDES, ONE OF SAID COATING CONSISTING OF INDIUM, A PRESSURE DEVICE HAVING TWO BODIES OF HEAT CONDUCTING METAL IN FACT-TO-FACE RELATION TO SAID RESPECTIVE ELECTRODE COATINGS, EACH OF SAID BODIES HAVIN A SURFACE COATING OF DUCTILE METAL, ONE COATING CONSISTING OF INDIUM AND BEING IN CONTACT WITH SAID INDIUM ELECTRODE COATING. 